1. Field
Embodiments of the inventive concept relate to semiconductor memory devices and, more particularly, to resistive memory devices.
2. Description of Related Art
Semiconductor memory devices, which are used to store data, may be classified into volatile semiconductor memory devices and nonvolatile semiconductor memory devices. A volatile semiconductor memory device may store data through charge or discharge of a capacitor, for example. A volatile semiconductor memory device, such as a random access memory (RAM), may store or read data when power supply is applied and lose data when power supply is interrupted. The volatile semiconductor memory device may be mainly used as a main memory device of a computer.
A nonvolatile semiconductor memory device may store data even if power supply is interrupted. The nonvolatile semiconductor memory device may be used to store programs and data for a wide range of applications, such as computers and portable communication devices.
Owing to the demand for fabrication of high-capacity low-power semiconductor memory devices, research has been conducted on advanced nonvolatile memory devices that do not require refresh operations. Currently, phase-change RAMs (PRAMs) using phase-change materials, resistive RAMs (RRAMs) using variable resistive materials, such as transition metal oxides, and magnetic RAMs (MRAMs) using ferromagnetic materials have attracted considerable attention as advanced memory devices. All of the advanced memory devices may have variable resistances according to applied currents or voltages and may not need refresh operations due to nonvolatile characteristics so that even if the currents or voltages are no longer applied, the advanced memory devices can retain the resistance value as it is.